BREP

BREP is the native shape file of the Open CASCADE kernel. A .brep file stores exact boundary-representation topology: vertices, edges, wires, faces, shells, and solids, carried by analytic curves and NURBS surfaces rather than a triangle mesh. FreeCAD's Part workbench and other Open CASCADE applications write it when a shape should be saved without converting it into a neutral exchange file.

Unlike STEP, this file is a kernel dump. It has no product structure, assembly metadata, materials, or textures. Closed solids are tessellated in the browser into a shaded mesh, and curves that were not sewn into a shell stay as wires. Use it to inspect an Open CASCADE shape you already have. Use STEP when the model has to move into SolidWorks, Fusion, or another CAD system.